Recovery of zinc from ores



June 5, 192s. Y' 1,672,616

R. T. D. WILLIAMS ET AL RECOVERY OF ZINC FROM ORES Filed Sept. ll, 19262 SheetF--Sheet l '5TM fara'.

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.im 5, 192s. L 1,672,016 R.` T. D. WILLIAMS ET AL RECOVERY OF ZINC FROMORES Filed Sept. 11, 1926 2 Sheets-Sheet 2 Patented June 5, 1928. j

UNITED sfrATEs PATENT OFFICE.

ROWLAND THOMAS DRYLI'; VJILLIAMS, OF HOBART, TASMANIA, AND STAFFORDWALCDO ROSS, OF CAMBRIDGE. NEAR HOBART,

AUSTRALIA, ASSIGNORS TO ELECTRO- LYTIG ZINC COMPANYOF AUSTRALASIALIMITED, OF MELBOURNE, AUSTRALIA.

RECOVERY 0F ZINC FROM OREb.

Application led September 11, 1926, Serial No. 134,835, and in AustraliaSeptember 1?, 1925.

This invention relates to certain improvements in the treatment of zincbearing ores for the' recovery of zinc bly electrolytic deposition andrefers more 'especially to that method of treatment wherein the orcs areleached with spent electrolyte containing sulphuric acid obtained fromthe electrolysis of zinc sulphate solutions, the liquors being'maintained in continuous circulation.

In the recovery ot' zinc by electrolytic deposition it has been foundthat the presence of salts of certain metals, such as cadmium and/orcopper interferes with and detrimentally allects the deposition of thezinc in the electrolytic cells and Avtor eiiectiv'e Working it isessential that the said metallic salts (generally regarded impurities)should be removed especially in View of the fact that some suchimpurities accumulate by the continuous circulation of the'solution.

One method of purification of zinc sulphate solution preparatory toelectrolysis vcomprises treatment with limestone for the precipitationof iron and other impurities and with linely divided zinc in the form ofzinc dust or blue powder for the precipita tion of any copper,cadmiunnsilver, arsenic,

antimony or other metals which would interfere-With the subsequentrecovery of the zinc In the treatment of these zinc bearing so lutionsthe aforesaid treatment with zinc dust or blue powder (usually known aszinc dust puriicat,fion) has usually been effectedf agitators. 'npractice it is the custom to feed a cert in quantity of the impuresolution into t e tank or vessel together With the requisite q, antit-yof zinc dust or blue powin large ve/els or tanks having mechanical derwhich/f' is considerably in excess of that theoretical-illy required forremoval ot the impurities present. The hatch of solution is maintainedin a constant state of agitation for the requisite time for" theprecipitation of the metals and other impurities it is desired toeliminate.

In practice care must be taken to have suilicient zinc present to ensurethat all of the metals or other impurities desired to be eliminated areprecipitated Whilst at the' same time undue prolongation of theoperation should be avoided to prevent the formation of an undue amount.ot basic zinc sulphate and thus consuming excessive zinc dust or there-solution of the cadmium due to oxidation. Consequently in practice.in order to obtain an economical result, this operation of purificationof the solutions by zinc. dust treatment must be care-fully controlledWhilst furthermore such intermittent treatment in batches invf. lves theexpenditure oi' a considerable amount of time and labour with theconsequent increase in operating costs. 'A

Now the object of this present invention is to provide certainimprovements in the treatment of zinc hearing ores ivherein` the zincbearing solutions are subjected to puri heat-ion by aine dust ior theelimination of certain metals and impurities preparatory to the recoveryot zinc by electrolytic deposition whereby considerable savings inoperating costs may he eected.

We accomplish the above object by Subjecting the impure zinc sulphatesolution to treatment with zinc dustin such manner that certain metalsand other impurities which interfere with the electrolytfic depositionof the zinc are eliminated during the flow' of the solutions incontradistinction to the batch treatment at present in vogue.

This purification during the flow of the solution is effected underclosed conditions whereby Contact with air and oxidizing con-I ditionsis avoided.

In carrying this invention into practical effect the impurezinc sulphatesolution together with zinc dust 'is passed more or less continuouslythrough an enclosed purifying chamber wherein the same is vigorously agitated, and then to a separating apparatus for separating the solutionscontainmg the pre cipitated impurities in suspension from une consumedzinc dust still under closed conditions, returning the said separatedunconsurned zinc dust to the inflow of the aforesaid purifying chamberand passing the separated solution containing the precipitatedimpurities in suspension to lter presses for removal and recovery of thecopper and cadmium precipitate, the above solution passing to theelectrolytic cells or other treatment for the recovery of'zinc.

In one method of adapting,r the invention to the electrolytic recoveryoi zine, the zinc bearing orcs are lirst roasted or calcined in theordinary Way for the elimination of sulphur. These roasted ores orcalcines are .then subjected. to treatmentwith spent vlecor blue powderadded to the clear sohnA tions whilst flowing more or less constanthYthrough a pipe or launder and the mixture is delivered into a series ot'closed pui-ilying vessels divided into a series ot' interconnectingcompartments within which it is maintained in a constant state ofagitation and through which the tlow is so nraintaim-d that therequisite time is allowed t'or the practically complete reaction of thezine dust upon the Salts otl the metals present and their precipitationenahling the soin-'- tion to be delivered at the lower end ot' theseries in a suitable. condition ior pass-incr io separating apparatuslor the separation ot the heavier and larger particles o't' unconsumedzi'nc dust from the hull; ot the solution containing the precipitatedimpurities. The solution containing the precipitated impurities issubsequently passed to tilter presses or Vother apparatus for theeliminaA tion ot the solid matter providing a soln .tion in a suitablecondition to Vhe l'ed to the elect-rolytic cells 'for the electrolyticdeposition of the zinc. l

The se arated unconsnined zinc dust or blue pow er is returned alone'with a qnantity of zine dust or blue powder equi 'aient to that Consumedin precipitating cadmium and copper to the pi ie or launder feeding theclosed purifying eliamher.

lin practice the apparatus preterahly consists of a long enclosed hor,placed hori- Zontally, divided h v vertical partitions into numerous'compartlnents` with suitahle passages provided for the purpose olEensuring the flow ot solution in 'series through the compartments. Thesepase fies are 5o placed as t0 minimize short-circmting of the solution.lh horizontal sha-tt rnnnincj through the apparatus carries agitatorolades in each compartment. Battles are ijnorided in eaoh compartment`to prevent the mere swirlingr of the solution and infr.. linpnresolution ed lazo he tirsi' compartment ot the seri, mud. at the sainetinte there is addr-tl the aniomtlzot 'flint' dust or hline powderlonnit nerr-sary l'or the required degree ol' parita-ation. .The puniherof crmipartnan s is ;;'r'1\'eijiied hy the time, required for theinipure lsolution to' pass directlyl throoglultw apparatus and hesuhiecitod to complete purilication. ln 'practiceit, has heen I'onndthatl from thirty-to forty compartments give satisfaction. and fartrule, can he given for the nuinher to ensure tl'iorongzh mix-- Thenuiuher and size of the compartments and the rate ol' tlow ot` solutionare so adjust'cd and controlled that the requisite period ot' agitationis .sn-h that practicallv complete precipitation ot the impurities iseffected hetween the intlow and the outflow without undue solution ofexcess :cine whilst re-solution ol' precipitated cadmium is avoided h vthe operation heilig carried out under non-oxidizing ef'niditions.

The Solution leaving;r the laat compartment is then i'cd into what istermed a separating apparatus wherein the larger particles of nnconsumcdzinc dust or hlne powder with Small amounts ot :nlherinpr precipitatednnpurities` are separated still without contact with air from themajority ot the precipitated iinpuritiea hy means ol gravity or ofcentrifugal action. 'iiie sepa rated solids are returned to the inletoi' the purifying chanaher in order to allo the nnconsuined zinc duet todo iurlher work.

The overtlow troni the separating apparatui= carries a small proportionof Solids in suspension which solids consist in the main ot' theprecipitated impurities. This solution is passed trom the separatingapparatus to litters or other menne i'or the removal of the .saidprecipitates without contact with air to ohtain a clear solutionnuit-able for feeding lto the electroiytic cells tor the deposition ot':eine therein.-

The ahow `method of `treatn'ient` is eontin` nous in operation and isetliected during the.

flow of the solutions and avoids the use ot',a

'consideralile -alnonnt ot time aind labour inhatch method cidenial tothe intermittent or of treatment as heretofore in practice.

in the following description ot' the process reference will he had tothe, accompany ing sheets ot' explanatory drawings wherein' one` forniot' apparatus adapted tor putting the process into rnacticalapplicationis il lnstrated and, in whichz 1figure l is a schematic Viewparatns.

Figure Q is a' View in side elevation (partly in section) ol" thepurifying cham? her.

Figure 3 a vil w in sectional end eleva-- tion laken on the dotted lino3-3 of Figure 2. v

Figure 4 is a view in sectional elevation. of part ot ihr fnirityingcharnhen Figure .ii is a view in sectional elevation oit the separatingapparatus.

Figure (l is a View in sectional plan of of the aplli) portion olthiseparatino apparatusand is of a constant hea i iced tank foreontroilingrv elevation Y lili.

Cil

tlio'los: of lligure solution to por lng chamber.

,he procrsS will! for aia' red 'n lie drawings l'ri car arrzr Soluti ,oi rrougfo lilo (lvlwry pipo il).

Tlv: So pasorl rough rho pipo l2 to the ld @ml of :i puri' vang chamber14 haring :i plurali@ oi giiiri'iliovs fiilvdiig it into a .aeries ofQompartirrmrts l5.

*lq sind short olisposorl respeciwly two .short pofifllcsare ada e loup;prrflilleg 18 from opoo-ie of rho szifr't l? and :i ar: .zr4 il. ato theslimpzrolos lil" and the pai'lrllm: are arranged alormimly :rt are endhrust ori rho shaft.

1a providing lxf? slim-l' paddles o lie con'l'ral pr' of ihr solu- :ioiimore or lof oquimlomly x ion of the solution in lle miler puri o 'liciirifying olml'nbor.

w pnrions 15 ire formed Wit-l1 jf-Qnlfglirougli which the shft isplaced. in :mfl which permit of lle solution g in fue purifying chamber.The of lli@ rompmlmen's z..f rmmflof io ma or 'o the w o of ho W bladesand he cornparizvir; are made su .cierily numerous. and of a and shapeas lo preven short circuiting of lio solution. laios Q iro arranged toproject from oppos@ sides oi" @sich 'partition and tires@ 'willoili'mlze the agitation of the solution bj; prev firing ho acon of thepaddles merely swirling.r it aroum the compiirments. Tho shui?, i7provided with the paddles 18 nml 1S may be made square in cross soctionsind is ondscm be connootw'l to Collinear slmft l which pass throughglands in thr- Sud@ o? the purifying Cl'imnhor 55ml are supporefl inbearings Q. Tho shaft and paddles are driven by belt and pulley roaringEl or in :my @flier approved way.

The soluion passes from ille last com pari'moit through o pipo 25 to rholower fend of :s ronively mouuofl Separating Chamb-or i255 ofcylindrical form.

The pipe WSS@ into :i` gliml 2T on fullo boitom of the separatingchamber and lie ranged i Such :z ratio allions por minuto v 32. ozi'emlsaxrerlly tliw gli-ri 28 and its lower iingl climi? ii 'le o out suffi ofs vusiljiv rm'ol'.'=-il relatively ing rliamoor,

Hw lower and of in lino will: the discr xml tapered 'fo delle :is iioilrrs the mlmmber 'w a ril fliei 52S and is l all n. gem wlw-Gli willia whe M to Countershaft 3G, A gear Whoo! El Cormier-s ft meshas Willifitted to @fue upper T lgearmf litter! to the gear Wlan-vl 3S hollowShaft rating fflmmbrr ronz 3j.. supporting ilmmuevs um! mmii worm willbe rotated in the sumo drocion zuid ai a lower rate of Speed.

Owing ro the lif'ferential speed. ha'mnes nml Worm revolvo slowlyrlaiwly "to the separaling Chamber and the said Worm moves :my solidmaierial at ilu: periphery of he bowl in a downward direction. 4

The solution fed through rho pip@ to the swarming Chmriber ih' pivkf-rlup lig' the vanos 53 amd firm A rapid Qrvulm move mout which resulte indie majority oi" the larger partidos oclug thrown io lie poriplr wy.

The souion is thus deplc'lwl of' its larger parioles out still retainsthe majority ofthe very line particles of the prmiptuted inlpuritics andthen emerges at the top of the sop iratiugz chamber through tho passages39 and into the top ofthe box L10 surrounding the said soparatingchamber. The sepafutod solidsl conveyed `downwar ls by the Bil umv

- trifugal pump 50 for the lower part of the box passing upwardlytherebeyond. The lower part of the -box 4() is provided with an outlet43 through which the4 larger particles and a certain amount of liquor inthe form of pulp pass to a hopper lll from which it is conveyed by anelevator' 45 to the constant head feed tank.

lThe speed of the separator is so adjusted that a requisite degree ofseparation between large and small particles is obtained. A speed whichis too high separates an excess of fine precipitated impurities whilst aspeed which is too lowyallows a portion of the larger zinc dustparticles to pass to the overow from the separator.

Experiment will readily determine the most satisfactory rate at whichthe separator is to be revolved.

The overflow frourthe separator passes through an outlet 46 in the topof the box /lO'and through a pipe +7 to a float chamber 4-8 having aconoida shaped bottom 48' which is connected by a pipe 49 to acendelivering the solution to filter presses, not shown.

The upper part of the box 40 extends above the separating chamber 26 andis provided With radially disposed baliies 5l which tend to prevent-thcsolution swirlingr around the same due to the action of the saidseparating chamber thereby permit-ting the solubulent condition through.the outlet pipe 4t?.

The Hoat chamber is provided with a float 52 having a stem 53 dependingfrom the centre thereof and terminating in a conical plug 54 which isadapted to seal the outlet when the solution reaches a low leveltherein.

When the tank is empty the weight of the float keeps the plug againstthe cone bottom and tends to seal the` discharge outlet therefrom and'as the solution enters it will lift the float and raise the plug toallow the solution to pass tothe pump casing.

Thus.y it will be understood that'the Hoa-toperated plug prevents thedrawing in of air at this point. i

lt will be obvious that the overflow from the separator may pass to alaunder for directin;r it to the float chamber. In' this case. thelaunder should be of comparatively large to obviate the solutionturbulently enteringr the floatchamber with the probar bility of itintroducing air.

The centrifugal pump should be designed to oliviate the drawing in ofair and this precaution is necessary since the precipitate suspended inthe solution the pump is handling is high in cadmium and low in metallic'/.inc and both of these factors are favorable to re-solution of cadmiumunder oxi- (lr/.ing conditions.

[n the foregoing description, where it is stated that the solutionshouid'iow to and tion to flow more readily and inl a less tur- .for

from the separator without turbulence it is intended to mean that theflow of the solution at these stages should be as tranquil as possibleand this' applies more especially in cases where antimony and/oi'arsenic is present in the solution.

The above process of treatment is continuous in operation andv iseffected duringthe iiow of the solutions and oliviates the use of aconsiderable amount of time and labour' incidental to the intermediateor batch method of treatment ordinarily employed.

In addition, whilst practically completo elimination of those metalscapable of being removed by zinc dust treatment is ei'ected, a" smallerquantity of excess of zinc dust is required. `and furthermore it hasbeen found that in practice coarser4 zin-c dust may be economically usedthan heretofore.

By the above method of treatment the factors necessary for theelimination of the impurities are put -into effect, namely, the rapidagitation with a maximum of Contact between the zinc dust or blue powderand the solution under non-oxidizing conditions ro that re-solution ofthe cadmium and con- A suinption of an undue excess of zinc dust isavoided; the presence of a'relatively large excess of zinc dust or bluepowder during the puriicat" n process' for the rapid precipitation of?Jthe impurities present and finally the rapid passage'of the solutionthrough the apparatus.

le have found that during rapid agitation -under the conditions 'as setout above the line particles of copper' and cadmium as precipitated onthe vsurfacel of the particles of the zincv'dust or blue powder are dislodged providing a fresh surface of zinc the precipitation of-further'.quantities of copper and cadmium. 1

The heavier aine dust particles separated at the bottom of\the separatorleave the cop, per and cadmium in suspension in the solution and thesettled zinc dust is returned to the irst compartment of the purifierfor use on fresh quantities of impure solutions 'While the copper and'cadmium precipitate remaining in suspension pass to the filter pressesfor'their separation from the clear solution. l

By this means the concentration of inetallic zinc in isbuilt. up to afairly high ligure so that by means of rapid agitation the actualpurifiwhich is essential for the prevention of the re-solution ofcertain metals such as cadmium and the consumption of an undue amount ofzinc dust.

ln practice it has been found that with a onsumption of P25-i507@ of theamount of nine dust theoretically required for thc. reduction of theimpurities present it, is practhe Apurifying vessels or tanks cation ofthe solution flowing therethrough `vis eli'ected in a minimum amount oftime iat impurities during the .flow of the. solutionr through theapparatus in Such a manner *lint tlieir contact witli the zinc dustranges over tlic period oi troni 3 to 5 ininotea. The time will varyaccording' io the size of tile agit-ating apparatus; the relative amountof zinc lust and imp rities present and the amount oi agitation giveniijuring purilication.

'We claim: i

i. in the treatment of zine-bearing ores for recovery of zinc, a processfor purifying Zinc suipiiate soiution which consists in' agitating 4suchsolution in tli-e presence of zinc dust under noiroxiriizing conditionsto @goot a precipitating reaction 'between Such dust and the impuritiesoi the soiution.

2. in the treatment oit zinc-bearing orcs forneco'vcrj;v of zinc. nprocces ior purifying' a cinc sulphate solution which consists incontinuously conveying and agit-ating such solution in the presence 'oi'zinc clust with exclu- Sion of air to effect. a Lnecipitating reactionloef-Ween such dust and the impurities of the solution.

3. ,in tire treatment of zincJJearing ores for recovery ot zincV` accntinuonev 'processi for purifying a liowing Zinc sulphate wluiionwhich consists in conriiinoiisly introducing zinc dust into the Rowingeoiution, agitating the -iioying oolution in the presence of suoli dustand in the absence of airto eiiect a precipitating, reaction betwcci'isuci'i dust and the impurities, and separating unconsumcd dust from theiiowing solution containing the precipitated impurities in suspension.

4. in he treatment of zinc--lfiearing ores for recovery ot' zinc, acontinuelle process for purifying a iiowizig; zinc suipliate solution,which consists in continuously introducing zinc dust into the towingsolution, agitzrtng the iowing solution in the presence of such dust andin the annonce of air to eii'ect a pre cipitating reaction between suolidust and ille. impurities, separating unconsuinori zinc dust from thel'iowing solution containing theprecipitated. impurities in Suspensionwith exclusion of air, and returning the separatori unconsumedv zincdust back into the solution from which the impurities-are to be'precipi' rated.

5. In the treatment of zincebearing for the recovery of zinc, acontinuelle procn ess for purifying a flowing :zinc .sulphate er lutionwhich consists in continuously introA ducing zinc dust into the fiowingSolutii agitating 'the owing solution in the. proI ence of such dust andin the absence o to effect a precipitating reaction between such ductand the impurities, separating` mr consumed zinc dustv from the flowing-Soiution containing'the precipitated impurities in suspension, andconveying said solution after separation of the unconeumed zinc duet`With exclusion of air to filtration.

. 6. ln the treatment of zii'ic-beuing ores for the recovery of zinc, acontinuous proccos for purifying a owing zinc sulphate soin tion whichconsists in continuously introduc ing zinc dust into tile lion/ingsoiut1on,'a,gi

tating the flowing soiution in the presence off such dust and in theabsence of air to eli' a precipitating reaction between Such di and theimpurities, and separating unconsunied zinc clust from tlic owingsolution containing the precipitated impurities in suspension withexcinsion of air.

T. In the treatment of Zinc-bearing orcs i'or the recovery of zinc, acontinuous process, for purifying a owing zinc suiphato solution whichconsists in continuouolyv intioducf.A

ing zinc 'dust into the fiowing solution, agie toting the flowingysolution in the presence of snc-li dust and in the absence of air toclfec't vprecipitating reaction between such clust and the impurities,separating unconsunied zinc dust from the iiowing solution containingthe precipitated inipuritee in .suspension with excinsion of air, androneyin@ :aid solotion :iiter separation of the unconeuuicr'i zinc dustwith exclusion of air to tilt ation in witness whereof we hereunto aliixour signatures.

ROWLAND THOMAS DRYLR WLLFAMS. STAFFORD WALD ROSS

